In general, handling means, particularly industrial robots may only be operated under closely defined conditions in the presence of people. Thus, safety devices for the operation of apparatuses with parts freely movable in space, particularly for industrial robots, have hitherto had a strict separation of the working areas of people and machines. As a rule use is made of protective devices such as e.g. fences.
If access to the working area is necessary as a result of the process, movable separating protective devices (such as e.g. protective doors or flaps) or non-separating protective devices (such as e.g. laser scanners, switching mats; according to protection category 3 or 4, DIN EN 954-1) are used, which detect an access by an operator to the robot working area during active operation and emit a signal, which trips an alarm or stops the danger-bringing movement. The prior art also includes manual operation with a consent button under reduced speed.
The aforementioned switching mats make use of the physical effects occurring during the distortion of an optical waveguide. A corresponding apparatus is known from DE 44 28 650 A1. In the case of an optical waveguide located in a contact mat in the case of a limited compressive stress there is a change to the modal distribution of the radiation field, so that an appropriately positioned light detector can measure with high sensitivity compressive forces.
CH 682 351 A5/EP 264 350 describes one of the numerous conventional apparatuses used for securing the working area of installations. It discloses a process-controlled installation with associated monitoring circuit and a safety circuit, which in particular has an access light and a door, by means of which access to the proximity of the robot is regulated and/or permanently monitored, so that in the case of an operator being positioned in the proximity thereof, only a stopping of the installation or creeping operation is possible.
EP 725 710 B1 discloses a further variant, in which an operator controls with a miniature model of the apparatus an apparatus movable in space through the starting of a miniature model of the object to be worked. A safety zone is defined around the apparatus in that the miniature model of the apparatus has a slightly larger scale than the object model. Collisions between the real apparatus and the object are supposed to be avoided “with absolute certainty.” Additional safety devices able to detect or prevent collisions are not disclosed.
Such protective devices on the one hand represent a considerable cost factor and on the other the commissioning costs are considerable.
EP 12 383 discloses an installation with movable parts, which is provided with an electrically conductive plastic layer, which in the case of compressive loading is placed in a real manner on the moving parts of the installation between two electrode layers. Between the resulting sensor system and the installation parts can be provided a deformable layer.
EP 689 903 discloses a robot with a coating of a viscoelastic material and on or below the surface are located pressure sensors for detecting collisions.
A capacitive sensor system is also known from DE 40 06 119 C2. This document relates to a capacitive displacement pick-up system with a capacitor controllable from the outside, which has an active electrode, a ground or earth electrode and a shielding electrode located between the active electrode and the ground electrode and which is at the same electrical potential as the active electrode.
A similar apparatus is known from EP 518 836 A1. WO 86/02506 relates to an approach detector of a capacitive nature for use in connection with elevator or lift doors. This document also discloses a capacitive sensor with a three-electrode arrangement, which also has a three-dimensionally directed detection sensitivity.
Such capacitive sensors measure capacitance changes, which are caused in the electric field of the capacitor formed by the sensor as a result of the approach of an object. In addition to all electrically good conducting materials, capacitive sensors only detect those materials having an adequately high permittivity.
The fact that a capacitive sensor system is unable to detect all material types is disadvantageous with respect to use as a safety device in the case of rapidly moving apparatuses with solid parts moved freely in space. In this connection a complete system is desirable, which permits a reliable human-machine cooperation.
The problem of the invention is to provide a safety device for the operation of apparatuses with parts freely movable in space, which permits the reliable and safe operation of such apparatuses without complicated and costly peripherals and which also ensures that collisions between apparatus parts and humans or objects are detected reliably at an early stage, so that in addition to avoiding planning and production costs there is a considerably reduced space requirement for such installations, so that in future people and machines can jointly use working areas.